Security systems which provide signals from a plurality of remote sending units and decode the signals in order to produce an appropriate alarm are known in the art. In certain of the prior art systems, a plurality of remote sending units transmit coded intrusion and other emergency signals to a central station. The station decodes the received signals and produces an appropriate response. However, the prior art does not adequately provide an alarm system for detecting a particular sequence and/or combination of events and providing flexibility to allow for several levels of response. The detection criteria of prior art systems also do not adequately provide for operator modification so as to tailor system response in light of current system requirements.
Furthermore, prior systems do not display at a control console in an easy to interpret manner the status of all current and past sensor detections and actions taken in response thereto. The user therefore does not have a complete system status report readily available at a control console. This complete status report is much needed if the user is to determine the criteria for initiating various actions in real time during ongoing system operation.
Additionally, prior systems do not provide the operator with the overall ability to disable any and all sensors, cut off automatic operation of any and all action devices, and manually initiate any and all action devices in real time during system operation. Consequently, the operator does not have total control and complete freedom to configure the system either for immediate system operation or for automatic operation over an extended period of time when the user is not present or does not desire to initiate manual control.
Often times the user is at a remote location and would like to be able to obtain system status. General purpose systems which only provide the status at a central location are not satisfying this requirement.
Conservation of RF frequency spectrum should be a goal of all systems just as is conservation of other limited resources. Systems should attempt to utilize the fewest transmission frequencies, the narrowest signal band width, and the shortest transmission period.
Most importantly, the data link between elements of the system must not appreciably raise the false alarm rate or lower the detection rate. The most common cause of loss in false alarm and detection rate is high noise and interference levels on the transmission path for the RF carrier frequency between the various data link senders and receivers. Such a data link might utilize the 60 Hz power line distribution system at the site where the data link is implemented. When no data is being sent and high noise and interference exist, the data link must suppress the passing or generation of spurious or false data. When data is being sent and noise and interference levels exist, the data link must preserve to the fullest extent possible the data message content without alteration.
A general purpose system is probably most needed during powerline outages. Thus, the data link must be capable of normal operation on batteries and without the 60 Hz powerline frequency for data synchronization purposes between transmitters and receivers.
The usefulness of a system is enhanced if the location and type of the remote sensor detections can be made known to a central location and if action commands from the central location can be directed at selected addressable receiver locations. This can be accomplished by digitally encoding the data link transmission with a suitably long digital address and command word. The digital word should be sufficiently long to prevent interference between a number of intruder alarm systems installed in the same neighborhood. Furthermore, to give the user unlimited full flexibility, each sender, receiver and central station where the processing of data is performed should have a built-in means to key any one of the total number of addresses permitted by the address word.
It is desirable that some systems utilize intruder detection sensors capable of detecting intruders before an entry is forced through a door, window etc. In such detectors which utilize frequency change detection mechanisms, it is necessary to overcome the tendency of the oscillator frequency to drift and the natural tendency of the least significant digits of a frequency counter to oscillate in order to insure an extremely low false alarm rate while maintaining a high detection rate.
These and numerous other problems which have not been satisfactorily solved by the prior art security systems are solved by the present invention.